Drilling systems are typically used to perform repetitive operations on the surface of assemblies with any shape and orientation, in particular aircraft fuselage assemblies.
Thus, American patent U.S. Pat. No. 5,468,099 describes a drilling system mounted on an self-contained mobile capable of moving on the curved surface of fuselage panels to be assembled. The self-contained mobile is used to assemble two panels, in particular to an internal structural beam of the aircraft. More specifically, the panels are arranged so as to substantially form a junction line between two respective ends of the panels, without there being any overlap. The self-contained mobile moves by creeping along the junction line and performs drilling operations for drilling fastening orifices. Then, the panels are fastened by riveting to the beam through the fastening orifices made.
However, several difficulties concerning the drilling appear when one seeks to assemble two panels, no longer through a beam, but directly to each other by an overlap area. Indeed, the relative mounting interference tolerances of the fastening members are very tight, in general a few hundredths of a millimeter only, such that it is extremely difficult to pre-drill the panels intended to form the overlap area of the two assemblies, while also ensuring the coaxiality of each of the holes in the interference tolerance. Consequently, the panels are generally arranged such that they are drilled during the same drilling operation, in order to obtain, during that same operation, a single orifice for housing the fastening member, formed by the two holes respectively obtained through the two at least partially superimposed panels.
The difficulty then lies in the fact that the assembly interface must in particular be free from any fins and any shavings for fear of reducing the fatigue behavior characteristics of the fuselage thus assembled. Moreover, to ensure the sealing of the interface between the assemblies, essential to the maintenance of the pressurization of the fuselage in flight, it is trimmed with a fine layer of a sealant, or interposition cement. Moreover, in order to ensure the mechanical transmission continuity of stresses in the fuselage, it is made such that the contact between the two assemblies at each fastening member is a metal-metal contact, i.e. there is no coupling of stresses through the interposition cement.
However, the drilling system of the self-contained mobile according to the prior art is equipped with a drilling tool that is not provided to avoid the formation of fins, or to make an assembly with metal-metal contact, at the interface between the two panels.
Thus, to ensure these different conditions, it is then necessary to                disassemble the two assemblies in order to perform cleaning and deburring of the panels at the fastening orifices;        apply the interposition cement on the panels of the assemblies intended to form the overlap area;        bring the two assemblies into position, to again bring these two assemblies into the determined relative position making it possible to put the fastening members in place, the two assemblies thus positioned jointly forming the overlap area having a layer of interposition cement between the two panels of said area.        
Thus, the inability of the drilling system according to the prior art to prevent the formation of fins, and to perform an assembly with metal-metal contact, at the interface between the two panels, requires the performance of disassembly/bursting and reassembly operations of the assemblies, as well as cleaning/deburring operations of the latter, which considerably lengthens the manufacturing cycle, making it expensive and not optimized.
To avoid the appearance of such fins at the overlap/junction area between the two panels having to be drilled during the same operation, one solution known from the prior art consists of applying a determined tightening force between these two panels. More precisely, the desired pressure is such that it makes it possible to generate a stress on the overlap area that prevents the appearance of fins on one hand, and the insertion of shavings at the interface of the assembled panels on the other hand, coated with interposition cement.
However, the means generally used to produce this pressure are complex and difficult to implement on the assemblies to be secured by seaming. Moreover, these pressurizing means make the intervention of a drilling system difficult, if not impossible, for bulk reasons.